IDT / ICS 3.3V LVPECL FREQUENCY SYNTHESIZER
13
ICS843004AG-02 REV A JULY 30, 2007
ICS843004-02
CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER
3. Calculations and Equations.
The purpose of this section is to derive the power dissipated into the load.
LVPECL output driver circuit and termination are shown in
Figure 6.
To calculate worst case power dissipation into the load, use the following equations which assume a 50
Ω load.
Pd_H is power dissipation when the output drives high.
Pd_L is the power dissipation when the output drives low.
Pd_H = (V
OH_MIN
/R
L
) * (V
DD_MAX
- V
OH_MIN
)
Pd_L = (V
OL_MAX
/R
L
) * (V
DD_MAX
- V
OL_MAX
)
Pd_H = (1V/50
Ω) * (2V - 1V) = 20mW
Pd_L = (0.4V/50
Ω) * (2V - 0.4V) = 12.8mW
Total Power Dissipation per output pair = Pd_H + Pd_L = 32.8mW
FIGURE 6. LVPECL DRIVER CIRCUIT AND TERMINATION
Q1
V
OUT
V
CCO
RL
50
V
CCO - 2V